As a result of an increasingly greater proportion of the population residing in cities with smaller homes and apartments, the housing of small pets presents additional problems. This is especially true of domestic cats which are confined indoors most of the time. As a result, the pet owner must provide for the animal waste materials, such as feces and urine. Most house-broken cats have learned to use a litter box which is generally a pan filled with an absorbent material, such as clay, wood chips, wood shavings, sawdust, porous polymeric materials, shredded paper, sand, etc.
A desirable absorbent for pet litter compositions possesses not only high moisture absorptivity, but also has a high absorptivity for odors, a low degree of dusting, adequate crush strength and a lack of toxicity to the pet. Granular clay pet litters have been available for approximately forty years and are typically 6/30 mesh size clays. These clays may be bentonite-type clays or attapulgite and typically, have been dried to a free moisture content of less than about 8 percent
An unpleasant chore faced by many pet owners is keeping the litter box clean so as to avoid unpleasant odors, spread of disease, etc. Generally, the feces can be merely separated from the absorbent material by use of a scoop or slotted spoon, but the liquid urine can spread throughout the absorbent material in the litter box and create a problem of odors and be a source of disease. As a result, the pet owner must discard the entire contents of the box after a relatively short period of use.
Recently, several products have been introduced that provide a clumping or agglomeration of the absorbent so as to form a clump of sufficient strength and integrity to be removed from the litter box and leave the unused absorbent material for further use. These products generally include an additive, such as a water absorbent polymer which clumps when contacted with the animal urine; see, for example, U.S. Pat. No. 4,685,420.See also U.S. Pat. No. 5,000,115 which proposes the use of a water-swellable bentonite clay which agglomerates and forms a stable mass upon contact with animal urine. The water swellable bentonite clays are described as being any member of the dioctahedral or trioctahedral smectite group, with montmorillonite being the most commonly known example. Although, attapulgite and sepiolite are also mentioned as examples of bentonite clay, these materials are not classified as bentonite clays by those skilled in clay technology.
The clumping litter materials which have been introduced over the past 5 years, are generally a finer absorbent material, typically being about 30/60 mesh. However, this presents disadvantages, since pets can track the 30/60 mesh more readily than the previously used granular 6/30 mesh products. Also, the clump's strength is often insufficient, and the clumps break up when the pets walk on them, or attempts are made to scoop the clumps up for removal from the litter. Further, those clumps that have high clump strength do not readily disintegrate in water and thus cannot be flushed in the toilet, and the chemical polymer additives which are sometimes used to improve clump strength, may impose an environmental hazard.
Other patents of interest, disclosing various clay-based animal litter compositions are U.S. Pat. Nos. 2,895,873, 3,029,783, 4,591,581 and 4,657,881. Several patents also describe use of various additives in animal litter compositions, primarily for controlling odor. See U.S. Pat. Nos. 3,352,792, 4,437,429, 4,407,231, 4,844,010, 4,949,672, 5,005,520 and 5,018,482.